Tracing PM-triggered GPU frequency changes from user space

Tracing PM-triggered GPU frequency changes from user space

[Heinrich Fink]

Hi,

is there a simple way for user space to trace PM-triggered changes of
GPU frequency on GEN9/Skylake? 

i915:intel_gpu_freq_change seems to only report SW-triggered frequency
change requests. The best option I currently see is to poll
gt_act_freq_mhz, but I was hoping for a more elegant solution.

Use-case: I am using GPUVis to understand problematic workloads of some
applications, and it would be useful to have the actual GPU freq
showing up in that trace along with the rest.

I found an old email thread [0] on this topic from 2012, but it's not
clear to me what eventually turned out to be the outcome of that
discussion.

Thanks,

Heinrich

[0] https://lists.freedesktop.org/archives/intel-gfx/2012-September/thr
ead.html#19951

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Re: Tracing PM-triggered GPU frequency changes from user space

[Chris Wilson]

Quoting Heinrich Fink (2017-11-14 12:19:28)
> Hi,
> 
> is there a simple way for user space to trace PM-triggered changes of
> GPU frequency on GEN9/Skylake? 

What is a PM-triggered change of gpu freq? Do you mean when the hw
itself throttles depending on thermal load. Then no. Best you can do is
use the i915 pmu interface to watch real vs requested.
-Chris
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Re: Tracing PM-triggered GPU frequency changes from user space

[Heinrich Fink]

On Tue, 2017-11-14 at 12:23 +0000, Chris Wilson wrote:
> What is a PM-triggered change of gpu freq? Do you mean when the hw
> itself throttles depending on thermal load.

yes, that's what I meant. Apologies for not being clear about this.

> Then no. Best you can do is
> use the i915 pmu interface to watch real vs requested.

Are you referring to the patch series "i915 PMU and engine busy stats"
[0]?

Thanks,

Heinrich

[0] https://patchwork.freedesktop.org/series/27488/
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Re: Tracing PM-triggered GPU frequency changes from user space

[Chris Wilson]

Quoting Heinrich Fink (2017-11-14 17:18:39)
> On Tue, 2017-11-14 at 12:23 +0000, Chris Wilson wrote:
> > What is a PM-triggered change of gpu freq? Do you mean when the hw
> > itself throttles depending on thermal load.
> 
> yes, that's what I meant. Apologies for not being clear about this.
> 
> > Then no. Best you can do is
> > use the i915 pmu interface to watch real vs requested.
> 
> Are you referring to the patch series "i915 PMU and engine busy stats"
> [0]?

Yes, that's the slightly more refined approached than polling sysfs.
-Chris
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